Actuator with Position Sensing Device

ABSTRACT

The invention relates to an actuator, in particular pneumatic cylinder, with an actuator element movably located in a movement space of a housing and with a microwave position sensing device for detecting the position of the actuator element in the movement space, with a microwave aerial arrangement for the transmission of microwaves into the movement space forming a waveguide and for the reception of reflection microwaves generated by the reflection of the transmitted microwaves at the actuator element from the movement space, and with evaluation means for the generation of a position signal representing the current position of the actuator element from the reflection microwaves. In the actuator, it is provided that the actuator element has a groove arrangement with at least one groove for reflecting the microwaves.

The invention relates to an actuator, in particular a pneumaticcylinder, with an actuator element movably located in a movement spaceof a housing and with a microwave position sensing device for detectingthe position of the actuator element in the movement space, with amicrowave aerial arrangement for the transmission of microwaves into themovement space forming a waveguide and for the reception of reflectionmicrowaves generated by the reflection of the transmitted microwaves atthe actuator element from the movement space, and with evaluation meansfor the generation of a position signal representing the currentposition of the actuator element from the reflection microwaves.

An actuator of this type is for example known from DE 198 33 220 A1 orfrom DE 10 2006 206.1, which is not subject to prior publication.

The actuator may for example be a pneumatic cylinder the piston of whichforms an actuator element installed for linear movement into a pistonchamber of the housing. The piston chamber or movement space iselectrically conductive on the inside, for example owing to a metalhousing, so that the movement space forms a waveguide. The microwavesspread from the aerial arrangement towards the piston and are reflectedby the piston. The evaluation means detect the position of the piston,for example using the reflection time between the outgoing microwave andthe returning reflection microwave.

The outer circumference of the piston is usually fitted with a seal madeof a dielectric material. As a result, the piston does not represent anideal waveguide short-circuit. There are further actuator elements orpistons made of plastic, which do not reflect the microwaves. Themicrowaves or waveguide waves then partially pass the actuator elementor piston and are only reflected by an end face of the movement spaceplaced opposite the aerial arrangement. As a result, the microwaves areentirely or partially reflected not by the actuator element as desired,but rather by an opposite end wall of the housing, so that the positionof the actuator element can only be detected with difficulty if at all.

The present invention is therefore based on the problem of improvingmeasuring accuracy in the detection of the position of the actuatorelement.

To solve this problem, it is provided in an actuator of the typereferred to above that the actuator element has a groove arrangementwith at least one groove for reflecting the microwaves.

The microwaves transmitted by the aerial arrangement are reflected withthe aid of the groove arrangement. Even a single groove improves thereflection characteristics of the actuator element. Expediently two,three or more grooves are provided.

The microwave aerial arrangement may for example transmit microwaves inthe so-called E01 mode or in the H11 mode in the circular waveguide. Ifthe transmitted E01 microwaves meet a coaxial obstruction, such as apiston, they are partially reflected or partially converted into acoaxial TEM wave. In this short section of coaxial conductor, the pistonrepresents the inner conductor, the seal between the piston and thecylinder wall the dielectric and the cylinder wall the outer conductor.If an H11 wave meets a coaxial obstruction, a field patterncorresponding to a higher mode in a coaxial line, i.e. an H11 wave in acoaxial line, is created.

The movement space expediently forms an outer conductor of a coaxialline for the microwaves, where the microwaves spread in the E01 or theH11 mode. The groove arrangement may for example be provided on an innerconductor section of the coaxial line. In this case, the groovearrangement impedes the current flow at the inner conductor section.Only a part of the current, if any, can flow across the groove. Thisresults in a local reflection of the electromagnetic wave and thus in anat least additional desirable reflection of the total wave impinging onthe actuator element.

The groove arrangement may be provided at different points of theactuator element. The groove arrangement is expediently located on anouter circumference of the actuator element. In this case, the groovearrangement may extend either over the entire outer circumference orover segments of the circumference of the actuator element. If thegroove arrangement extends over segments of the circumference, theactuator element is advantageously secured against rotation in themovement space.

The at least one groove or the groove arrangement could howeverconceivably be provided on a recess or a projection of the actuatorelement. An actuator element may obviously comprise several groovearrangements, for example on an outer circumference, a projection or thelike. The grooves on the projection or recess may extend over a part orsegment of the circumference or over the entire outer circumference ofthe projection or the entire inner circumference of the recess.

By means of the groove arrangement, the movable actuator elementreflects the microwaves, which may for example be coupled into themovement space with the aid of a coupling probe of the microwave aerialarrangement. Using a reflection time measurement and/or a phasecomparison between transmitted and received microwaves, which may have afrequency range of 10 MHz to 25 GHz—preferably 1 GHz to 25 GHz—theposition sensing device detects a position of the actuator element inthe movement space. The position sensing device may for example measurethe distance of the actuator element from an end stop in the region ofthe microwave aerial arrangement.

The actuator, which may be an electric or fluid-powered drive, has ahousing with an electrically conductive movement space in which anactuator element, for example a rotor of an electric motor or a pistonof a pneumatic drive, is movably installed. The actuator expediently isa linear actuator. In this case, the actuator element is capable oflinear movement. The principle of the invention can, however, also beapplied to a rotary or semi-rotary actuator.

The actuator may be driven electrically and/or by fluid power, forexample pneumatically or hydraulically. A so-called hybrid drive withboth electric and fluid power operation is also advantageous.

In a further variant of the invention, it may be provided that theposition sensing device is a part of a fluid valve, for example apneumatic valve. In this case, the actuator element is the valve memberof the fluid valve, for example a drive piston by which the valve memberis driven pneumatically.

The groove may for example have a rectangular internal contour. The baseregion may for example have a rectangular shape. Polygonal, V-shaped,U-shaped or circular internal contours are obviously conceivable aswell.

The recess or projection with the groove arrangement may form a part ofa cushion arrangement for the reduction of the end-of-stroke speed ofthe actuator element in the region of an end stop of the housing or themovement space. The groove arrangement for example comprises a recess oris located on a recess into which a projection on the housing can dip.This projection may for example be a part of a cushion arrangement. Asthe actuator element approaches the end stop, the projection on thehousing engages the recess in the actuator element, or the projection onthe actuator element engages the recess of the housing and blocks afluid passage provided for the entry and discharge of fluid. Now thefluid, for example compressed air, can only flow out in a restrictedmanner through an outlet passage, thus reducing the end-of-stroke speedof the actuator element in the region of the end stop.

The recess or the projection with the groove arrangement according tothe invention and the microwave aerial arrangement are expedientlycoaxial.

The at least one groove may be hollow or filled with a dielectricmaterial. The groove arrangement may comprise both hollow grooves andgrooves filled with a dielectric material. A groove may furtherconceivably be partly hollow and partly filled with a dielectricmaterial. The dielectric material, for example plastic, rubber or thelike, may be applied to the actuator element by injection moulding.Alternatively, the dielectric material may be a separate componentfitted to the actuator element in an assembly process.

The depth of the at least one groove is expediently approximately ¼ ofthe wavelength of the microwaves spreading in the region of the interiorof the at least one groove. The interior may for example be hollow, sothat the microwaves have a wavelength corresponding to propagation inair. As explained above, however, the interior may be wholly orpartially filled with a dielectric material. In this case, the depth ofthe at least one groove is expediently determined by the dielectricconstant of the material. The depth of the groove is expediently lessthan ¼ of the wavelengths of the microwaves with reference to air aspropagation medium. The wavelength of the microwaves in air may forexample be λ0; the wavelength λ of the microwaves in the region of thedielectric in the at least one groove is calculated as follows.

$\begin{matrix}{\lambda = \frac{\lambda \; 0}{\sqrt{ɛ\; r}}} & (1)\end{matrix}$

wherein ∈r is the dielectric constant of the dielectric material. Thedepth of the grooves may for example be 2 mm to 5 mm.

The spacing of the grooves of the groove arrangement is expediently lessthan the depth of the grooves themselves. It may for example besignificantly less than ¼ of the wavelength of the microwaves. Asexplained above, the wavelength of the microwaves is determined by thedielectric used, for example air or plastic. The spacing and the depthof the grooves are matched to the operating frequency of the microwaves.

In one variant of the invention, the grooves of the groove arrangementmay be provided on the actuator element exclusively for reflectionpurposes. Alternatively, the groove arrangement may conceivably act asor include a holder for at least one further component of the actuatorelement. One or more grooves may for example be provided to form a sealarrangement or a device for guiding the actuator element. The groovesmay further conceivably include separate retaining grooves for theretention of the further component, for example the seal arrangement.The further component, for example a sealing ring or the like, mayalternatively engage only a part-section of the groove of the groovearrangement.

The actuator element may comprise a plastic actuator body on which thegroove arrangement is located. The groove arrangement may for example beprovided on an electrically conductive component on the plastic actuatorbody. This component may for example be a sleeve installed into alocation of the plastic actuator body or projecting from the plasticactuator body.

The groove arrangement may further include an electrically conductivecoating on the actuator element. The actuator element may for example beprovided with grooves, for example produced by milling, which are givenan electrically conductive coating. It is further conceivable that aplastic component with the groove arrangement is fitted to the actuatorelement, the grooves of the plastic component being provided with theconductive coating.

Embodiments of the invention are explained below with reference to thedrawing. Of the drawing:

FIG. 1 is a cross-sectional view of a pneumatic cylinder with a pistonhaving grooves arranged on its outer circumference;

FIG. 2 is a cross-sectional view of a pneumatic cylinder with acushioning projection having grooves arranged on its outer circumferenceprovided on a piston;

FIG. 2 b shows a piston which can be installed into the cylinderaccording to FIG. 2 as an alternative;

FIG. 3 a is a diagrammatic cross-sectional view along line A-A of thecylinder from FIG. 2 with microwaves in the E01 mode;

FIG. 3 b is a diagrammatic cross-sectional view along line B-B of thecylinder from FIG. 2 with microwaves in the TEM mode;

FIG. 4 is a cross-sectional view of a rodless operating cylinder with arecess where the grooves are provided;

FIG. 5 a is a cross-sectional view of the operating cylinder accordingto FIG. 4 along line C-C with microwaves in the H11 mode;

FIG. 5 b is a cross-sectional view of the cylinder according to FIG. 4along line D-D with H11 microwaves as the higher mode in a coaxial line;

FIG. 6 a is a cross-sectional view of a piston of a pneumatic operatingcylinder according to prior art;

FIG. 6 b is a cross-sectional view of a piston resembling theconstruction shown in FIG. 6 a, but provided with grooves according tothe invention;

FIG. 7 is a cross-sectional view of a piston with hollow grooves on itsouter circumference; and

FIG. 8 shows a piston of an operating cylinder with grooves partiallyfilled with a dielectric material.

Similar components of the embodiments described below or components ofsimilar action are identified by the same reference numbers anddescribed only once.

A pneumatic operating cylinder 11 a forms an actuator 10 a, inparticular a fluid-power actuator. In a movement space 12 of an actuatorhousing 13 a, an actuator element 14 a capable of linear reciprocatingmovement is located. The actuator element 14 a is represented by apiston 15 a of the operating cylinder 11. The illustrated embodiment isa pneumatic operating cylinder with a piston rod, but rodless variants,electric drives or combined electro-pneumatic drives, in particularlinear drives, are possible alternatives.

A valve assembly 16, for example comprising a 2/2-way valve, feedscompressed air 17 from a compressed air source 18 through pneumaticports 19, 20 into the movement space 12 or allows compressed air to bedischarged from the pneumatic ports 19, 20 to drive the piston 15 a,which divides the movement space 12 into two part-chambers notidentified in detail. For this purpose, a seal 21 a is for exampleprovided on the outer circumference of the piston 15 a.

An end face of a central part 22 of the housing 13 is sealed by abearing cap 23 a and a cover 24 a, thus bounding the movement space orpiston chamber 12. A piston rod 25 forming a power take-off element ofthe operating cylinder 11 a passes through the bearing cap 23 a at anopening 26 provided with a seal.

A position sensing device 50 is provided to detect the position of theactuator element 14 a within the movement space 12, for example adistance 28 of the piston 15 a from an end stop 27 on the cover 24 a.

The microwave aerial arrangement 51 for example comprises a couplingprobe for transmitting and receiving microwaves at a high frequency, forexample in a frequency range of approximately 10 MHz to 25 GHz. Thecoupling probe may be a metallic probe or a plastic element withelectrically conductive surfaces.

The microwave aerial arrangement 54 is connected to a high-frequencydevice 52, for example a high-frequency circuit board or the like, andto an evaluation device 53.

With the aid of the high-frequency device 52, microwaves 54 can begenerated to be coupled into the movement space 12 by the microwaveaerial arrangement 54. The movement space 12 forms a waveguide 56 whichguides the microwaves 54 to the actuator element 14 a, which reflectsthe microwaves 54 and generates reflection microwaves 55.

The microwave aerial arrangement 51 may be located in a dielectricsection of the cover 24 a. Apart from that, the cover 24 a isexpediently made of metal. The central part 22 and the cap 23 a areexpediently also made of metal. In any case, an inner wall 29 of thecentral part 22 is electrically conductive to form the waveguide 56.

The high-frequency device 52 comprises input elements and outputelements not identified in detail, such as capacitors, millimetre waveintegrated circuits (MMICs), directional couplers or the like. Thehigh-frequency device 52 is advantageously able to transmit themicrowaves 54 in different frequencies and in further frequencies notidentified in detail, for example with the aid of a voltage-controlledoscillator (VCO) or the like.

The high-frequency device 52 and the evaluation device 53, whichcomprises or represents evaluation means according to the invention, areelectrically connected to one another and may be fitted to a commonsupport structure. The high-frequency device 52 and/or the evaluationdevice 53 may be located in or on the cover 24 a.

Using the reflection time of pulses of the microwaves 54, 55 (pulseradar), the phase shift between outgoing microwaves (54; 54′) andreturning microwaves (55) (interferometer method), an FMCW (frequencymodulated continuous wave) process or the like, the evaluation device 53determines the position, which may for example correspond to thedistance 28 of the actuator element 14 a within the movement space 12.The evaluation device 54 and/or the high-frequency device 52 may forexample comprise a mixing device for mixing, for example multiplying,the transmitted microwaves 54 and the reflected microwaves 55, aprocessor, a memory and/or further electronic components, such as ASICs(application specific integrated circuits) or the like. The evaluationdevice 53 transmits a position signal 57 representing the currentposition of the actuator element 14 a to a superior control unit S bywireless means, for example using an aerial 58, or via a line 59.

On an outer circumference 30 of an actuator body 31 a, for example ametal body or an electrically conductive, for example coated, plasticbody, a groove arrangement 32 a with grooves 33 a is provided.

The electrically non-conductive seal 21 a would allow a partialpenetration of the microwaves 54 into the space behind the piston, whichwould be undesirable. The groove arrangement 32 a, however, reflectsvirtually all of the microwaves 54, so that the reflection microwaves 55are generated.

The depth 34 a of the grooves 33, which may have a rectangularcross-section, is matched to the frequency or wavelength of themicrowaves 54. This takes account of the dielectric quality of the seal31 a extending into interior spaces 35 of the grooves 33 a. The depth 34a may for example be ¼ of the wavelength of the microwaves 54 in theregion of the interior spaces 35, the wavelength of the microwaves beingreduced in the region of the interior spaces 35 in dependence on therelative permittivity of the material for the seal 21 a.

A pneumatic operating cylinder 11 b includes some components which areidentical with or similar to those of the operating cylinder 11 a.

On a cover 24 b, a cushion arrangement 36 b is provided to cushion theimpact of a piston 15 b representing an actuator element 14 b on an endstop 27 in the region of the cover 24 b. As the piston 15 b approachesthe end stop 27, a cushioning projection 37 projecting in front of thepiston 15 b dips into a recess 38 in the region of the cover 24 b or ona cushioning ring 38′ placed in front of the cover 24 b in a finalmovement section. Now compressed air can no longer flow out of themovement space or the piston chamber through a passage 39. Air can onlybe discharged from the movement space 12 through an outlet passage 40. Apreferably adjustable restrictor 41 is expediently provided on theoutlet passage 40. The reduced cross-section of the outlet passage 40cushions the stroke of the piston 15 b in the region of the end stop 27.

The cushioning projection 37 is provided with a groove arrangement 32 bwith grooves 33 b. the groove arrangement 32 b reflects the microwaves54 to generate the reflection microwaves 55.

The grooves 33 b are formed on a groove component 42 located on aprojection body 43 of the cushioning projection 37. The groove component42 may for example be sleeve-like. The grooves 33 b are provided on anouter circumference of the groove component 42. The projection body 43may for example be made of plastic or of another dielectric material.The groove component 42 is electrically conductive at least in theregion of the groove arrangement 32 b, for example being provided withan electrically conductive coating or because the groove component 42 ismade of metal.

The grooves 33 b may alternatively be provided on an outer circumferenceof a projection body 43′ of a piston 15 b′, which can replace the piston15 b. The projection body 43′ may be made of metal. The grooves 33 b arefor example milled in.

The interior spaces 35 of the grooves 33 b may be filled with adielectric material 47. In this case, the depth 34 b of the grooves 33 bwould be less than if they were “only” filled with air.

The microwaves 54, 55 spread in the region between the end stop 27 andthe cushioning projection 37 in the E01 mode (FIG. 3 a) while changingat least partially to the TEM mode (FIG. 3 b) in the region of thecushioning projection 37.

An actuator 11 c is represented by a pneumatic operating cylinder. Theoperating cylinder 11 b is a so-called rodless operating cylinder, i.e.no piston rod is fitted to the actuator element 14 c represented by apiston 15 c. The piston 15 c is capable of linear reciprocating movementin the movement space 12 between the covers 23 c, 24 c. Cushionarrangements 36 c, 36 c′ are provided on the covers 23 c, 24 c. Passages39 lead from the pneumatic ports 19, 20 to cushioning projections 37 con the covers 23 c, 24 c. The compressed air flows through the passages39 into the movement space 12 or is discharged therefrom to drive thepiston 15 c.

As the piston 15 c approaches the end stops 27 adjacent to theprojections 37 c, the projections 37 c dip into recesses 38 c, 38 c′ inthe piston 15 c in a last movement section before reaching the end stops27. This blocks the passages 39, allowing no further air to flow intothe inlet or outlet port of the discharge-side passage 39 on theprojection 37 c. The air now flows out of the movement space 12 throughoutlet passages 40 terminating in the passages 39. The passages 40 arepreferably fitted with adjustable restrictors 41.

A position sensing device 50′ generates microwaves 54′ in the so-calledH11 mode with an aerial arrangement 51′. The aerial arrangement 51′ isprovided on the cover 24 c, preferably in a dielectric region. FIG. 5 ashows the microwaves 54′ in a section between the end stop 27 and thepiston 15 c. In the region of the recess 38 c, the microwaves 54′ becomeso-called H11 waves as a higher mode in a coaxial line.

A groove arrangement 32 c with grooves 33 c is provided in the recess 38c′. The grooves 33 c reflect the microwaves 54′.

The grooves 33 c are provided on an outer circumference of a metallicsleeve 44. The sleeve 44 contains the recess 38 c′ for the cushioningprojection 37 c. In principle, grooves 33 c on the outer circumferenceof the sleeve 44 would be sufficient. The sleeve 44 may for example bemade of metal. In the present case, a base 45 of the sleeve 44 is madeof metal as well. The electrically conductive base region 45 is howevernot required.

The piston 15 c comprises an actuator body 31 c on which the sleeve 44with the groove arrangement 32 c is located. The sleeve 44 may forexample be installed into a recess 46 on the actuator body 31 c, whichmay be made of plastic or metal.

There are no grooves on the recess 38 c on the side of the piston 15 cwhich is remote from the aerial arrangement 51′.

In principle, grooves could be provided, for example by milling, on therecess 46 for the sleeve 44 rather than on the sleeve 44 itself, whichis an electrically conductive component on the actuator body 31 c. Ifthe actuator body 31 c is made of plastic, these grooves may for examplebe given an electrically conductive coating, for example using aphysical or chemical vapour deposition process (physical vapourdeposition/PVD; chemical vapour deposition/CVD).

There are no grooves or groove arrangements on the outer circumferenceof the pistons 15 b, 15 c. The outer circumference of the pistons 15 b,15 c is fitted with seals 21 b, 21 c.

In place of the piston 15 a, a piston 60 as shown in FIG. 6 b could beused. The piston 60 has an annular piston body 61 with a location 62,for example for the piston rod 25. On the outer circumference of thepiston body 61, a central slot 63 is located between slots 64. The slots63, 64 are circumferential grooves. The central slot 63 accommodates anannular magnet 71 provided for triggering conventional position sensorssuch as magneto-restrictive sensors or Hall elements. The lateralannular slots 64 are grooves 65 of a groove arrangement 66 provided toreflect microwaves.

The piston body 61 is extrusion-coated with an elastic sealing materialforming a seal 67. The seal 67 is made of a dielectric material andfills the grooves 65. The seal 67 comprises seal sections 68 extendingradially outwards at an angle, which may for example bear tightlyagainst the inner wall 29. Between the annular seal sections 68, arecess 69 for a guide band 70 is provided.

A piston 60′ shown in FIG. 6 a is a conventional piston without anygrooves 65 for reflecting microwaves. A piston body 61′ of the piston60′ is only provided with the central slot 63 for accommodating themagnet 71.

In place of the piston 15 a, a piston 75 according to FIG. 7 could beused. Grooves 76 of a groove arrangement 77 are provided on the outercircumference of the piston 75. The grooves 76 are continuous annulargrooves. If the piston 75 were secured against rotation but capable oflinear movement in the movement space 12, for example owing to apolygonal cross-section of the movement space 12 or owing to theprovision of a guide arrangement, such as a longitudinal slot for thepiston 75, the grooves 76 could conceivably extend only over a part ofthe circumference of the piston 75.

The grooves 76 have a rounded base region. The grooves 76 are providedon an outer circumference of an actuator body 78 which may for examplebe made of metal. The grooves 76 are substantially hollow.

The outer circumference of the actuator body 78 supports a seal 80, forexample an O-ring, which seals the grooves 76 radially on the outside.

The depth 79 of the grooves 76 is greater than a depth 79′ of grooves76′ of a groove arrangement 77′ on an actuator element 75′. The grooves76′ are partially filled with a dielectric material, which may berepresented by sections of a seal 80′ of the actuator element 75′ whichproject radially inwards.

It is understood that the invention can also be implemented in anelectric drive or an electro-fluidic hybrid drive. The piston 60′ withits magnet 71 could for example be driven by a field coil arrangement100 as shown for the actuator 10 a by way of example. The field coilarrangement 100 forms an electric drive component 101 for driving theactuator element 101.

1. An actuator comprising: a pneumatic cylinder; an actuator elementmovably located in a movement space of a housing; a microwave positionsensing device for detecting the position of the actuator element in themovement space, a microwave aerial arrangement for the transmission ofmicrowaves into the movement space forming a waveguide and for thereception of reflection microwaves generated by the reflection of thetransmitted microwaves at the actuator element from the movement space;and evaluation means for the generation of a position signalrepresenting the current position of the actuator element from thereflection microwaves, the actuator element having a groove arrangementwith at least one groove for reflecting the microwaves.
 2. The actuatoraccording to claim 1, wherein the waveguide acts as an outer conductorof a coaxial line for the microwaves and the groove arrangement islocated on an inner conductor section of the coaxial line, the groovearrangement at least partially preventing a current flow along the innerconductor section and thus acting as a reflection body.
 3. The actuatoraccording to claim 1 wherein the groove arrangement is located on anouter circumference of the actuator element.
 4. The actuator accordingto claim 1 wherein the groove arrangement is located on a recess of theactuator element.
 5. The actuator according to claim 1 wherein thegroove arrangement is located on a projection of the actuator element.6. The actuator according to claim 5, wherein a recess of the actuatorelement or the projection forms a part of a cushion arrangement forreducing the end speed of the actuator element in the region of an endstop of the housing.
 7. The actuator according to claim 1 wherein thegroove arrangement has a recess or is located on a recess into which aprojection on the housing can dip.
 8. The actuator according to claim 3wherein the groove arrangement is provided on the entire outercircumference or at least on a segment of the circumference of theactuator element or of the projection of the actuator element or on theentire inner circumference or at least on a segment of the innercircumference of a recess of the actuator element.
 9. The actuatoraccording to claim 1 wherein the groove arrangement and the microwaveaerial arrangement are coaxial.
 10. The actuator according to claim 1wherein the at least one groove has a rectangular internal contour. 11.The actuator according to claim 1 wherein the at least one groove ishollow or filled with a dielectric material.
 12. The actuator accordingto claim 1 wherein the at least one groove has a depth corresponding toapproximately a quarter of the wavelength of the microwaves spreading inthe region of the interior space of the at least one groove.
 13. Theactuator according to claim 12, wherein the interior space is filledwith a dielectric material and the depth of the at least one groove isless than a quarter of the wavelength of the microwaves with referenceto air as propagation medium.
 14. The actuator according to claim 1wherein the spacing of the grooves of the groove arrangement is lessthan the depth of the respective grooves.
 15. The actuator according toclaim 1 wherein the groove arrangement forms or includes a holder for atleast one further component of the actuator element, in particular for aseal arrangement and/or for a guide device for guiding the actuatorelement in the movement space.
 16. The actuator according to claim 1 theactuator element comprises an actuator body, in particular a plasticactuator body, on which the groove arrangement is located.
 17. Theactuator according to claim 1 the groove arrangement is located on anelectrically conductive groove component provided on the actuator body.18. The actuator according to claim 1 wherein the groove arrangementincludes an electrically conductive coating provided on the actuatorelement.
 19. The actuator according to claim 1 wherein the actuator itis a rodless pneumatic operating cylinder or a pneumatic operatingcylinder with a piston rod.
 20. The actuator according to claim 1wherein the actuator comprises an electric drive or an electric drivecomponent.